async_io_dispatcher_base::enumerate() did not take a metadata_flags, and it was supposed to. Thanks to Bjorn Reese for reporting this.

Added a unit compilation test to ensure that implicit construction from a single arg to the op convenience classes works as intended.

Significantly optimised build system and added in precompiled headers support. Combined with --fast-build this provides an 8x build time improvement.
Updated docs.
Minor typo fix.
Merge branch 'master' of github.com:BoostGSoC/boost.afio